As transistors continue to decrease in size, transistor density within electronic components continues to increase. While increases in transistor density provide many desirable effects, such as a reduction in component size and a reduction in power consumption, it may also create problems. Such problems may include increased power consumption, unwanted heat generation, and device reliability issues. Several methods have been devised to counter these problems so that transistor density may continue to increase without creating undesirable side effects. One such method is utilizing level shifter circuits.
Level shifter circuits may enable different digital logic components to operate at different power supply voltages. Operating in different logic voltage ranges serves to increase device reliability, decrease power consumption, and lower excess heat generation by providing specific voltage ranges to specific digital logic components. By limiting specific components to specific operating voltages, power consumption and heat generation may be easier to control and device reliability may be increased. Utilizing different logic voltages also presents significant problems as a digital high or low for one digital logic component may not have the same voltage values for another digital logic component. Therefore, it may be difficult or even impossible for components with different voltages to operate together. Level shifter circuits may serve as interfaces (or voltage translators or converters) between different logic device components to shift the voltage level of one component to an appropriate level of a second component to ensure adequate coherence between the voltage levels of the two components.
Level shifter circuits typically take one voltage value and shift it to a second voltage value. Level shifters can shift both up and down, and examples are depicted in FIGS. 1A and 1B. The level shifter circuit in FIG. 1A only utilizes cross-coupled P-type devices to shift an incoming digital signal, d, to a higher logic voltage range at output y. The level shifter circuit depicted in FIG. 1B utilizes a current mirror configuration to shift an incoming data signal, d, to a higher data range at output y. These sample level shifter circuits are capable of translating a digital logic signal with a small amplitude to a full-swing digital signal, but are limited in their capabilities. These circuits, however, are limited in their capabilities. For example, they are not capable of shifting to one or more other power supply voltage levels or supporting voltages higher than a base power supply level while utilizing transistors rated only for the base power supply level.
What is needed, therefore, is a level shifter circuit that can translate a digital logic signal from one power supply level to one or more power supply levels while only utilizing transistors rated for the base power supply level. What is also needed is a level shifter capable of shifting an input logic signal to various voltage ranges wherein the various voltage ranges are multiples (or divisors) of a base power supply voltage and supporting high voltages that are multiples of the base power supply while utilizing transistors rated for only the base power supply.